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Full text of "Handbook Of Chemical Engineering - I"

EVAPORATION
391
to lower the temperature and the mixing should always be done after the combustion is completed to avoid fuel losses. Similar rotating dryers are' also used for hot air, and frequently the interior of the drum is fitted with plates and baffles to afford a better contact between the air or gas, and the material to be dried.
A special type of dryer is shown in Fig. 30.    It can be used for liquids or thin
FIG. 30.—Dryer for liquids or thin pastes.
pastes only, and these are picked up by an endless wire apron which passes through the various chambers of the dryer continuously. . After the drying process is completed, the material is removed from the flexible wire netting by breaker rolls and brushes. Generally the efficiency is good, as the fire or waste gases are utilized to the fullest extent, on account of the long contact with the material.
FIG. 31.—Pan dryer, steam-heated.
Drying by Steam and Hot Water.—In dryers of this type, the heat is transferred through metallic surfaces, and where liquids are to be dried, calculations may be based on the equations given in the previous chapter on "Heat Transmission/' But where moisture is to be removed from solids, we have to resort again to experiments and tests in order to determine the capacity of a certain